1. Field of the Invention
The present invention relates to a copper foil used as a current collector of a lithium secondary battery, and more particularly to a copper foil for a current collector of a lithium secondary battery, which has a structure capable of preventing the generation of wrinkles on a surface of the copper foil.
2. Description of the Related Art
A lithium secondary battery has many advantages such as high energy density, high operation voltage, excellent preservation and excellent life cycle in comparison to other kinds of secondary batteries, so the lithium secondary battery is widely used for various portable electronic devices such as personal computers, camcorders, cellular phones, portable CD players and PDA.
A lithium secondary battery generally includes a cathode and an anode, which are arranged with a separator being interposed between them, and an electrolyte. The cathode and the anode respectively include cathode active material and anode active material, and a cathode current collector and an anode current collector respectively contacted with the cathode active material and the anode active material.
In the lithium secondary battery, a copper foil is mostly used as material of the anode current collector, and the copper foil is generally coated with active material such as carbon-based slurry. Here, the copper foil is made by making an electrodeposited copper foil by means of electroplating and then conducting a post-processing to give peel strength to the original foil. A so-called shiny side is formed on one surface of the electrodeposited copper foil by means of electroplating in accordance with a surface shape of a drum of a foil making machine, and a matte side having a relatively high surface roughness due to a mountain structure is formed on the other side of the electrodeposited copper foil. Also, the electrodeposited copper foil is additionally coated with a protective layer at a post-processing so as to ensure corrosion resistance and color fastness.
Battery characteristics of a lithium secondary battery are greatly changed in accordance with a surface state of a copper foil used as a current collector, so it is very important to improve surface characteristics such as wrinkle characteristics in order to improve a yield.
In case a wrinkle exists on a surface of a copper foil as shown in FIG. 1, active material is not uniformly coated due to the irregularity of the surface shape, which may cause a short-circuit or separate the active material from the copper foil during a charging or discharging process.